merge JSON objects without new keys

Question

How to merge two JSON objects but do not include properties that don't exist in the first Object?

Input

var obj1 = { x:'', y:{ a:'', b:'' } };
var obj2 = { x:1, y:{ a:1, b:2, c:3 }, z:'' };

Output

obj1 = { x:1, y:{ a:1, b:2 } };

ps. There is a method for Objects called preventExtensions but it appears to only block the immediate extension of properties and not deeper ones.

Phrase the question in the question, post the answer as an answer, and accept it. — Rob W
– Rob W, Commented Nov 3, 2011 at 15:18
@vsync: It's a great idea to post solutions to help other people in the future, but you should format it as follows; 1) Post a question "pretending" to ask the question, 2) post your solution as an answer to your own question, and accept your own answer as the solution. Who knows, you might even get another answer giving a different (better?) approach! — Matt
– Matt, Commented Nov 3, 2011 at 15:18

vsync · Accepted Answer · 2011-11-03 17:54:15Z

4

/*
    Recursively merge properties of two objects 
    ONLY for properties that exist in obj1
*/

var obj1 = { x:'', y:{ a:'', b:'' } };
var obj2 = { x:1, y:{ a:1, b:2, c:3 }, z:'' };

function merge(obj1, obj2) {
    for( var p in obj2 )
        if( obj1.hasOwnProperty(p) )
            obj1[p] = typeof obj2[p] === 'object' ? merge(obj1[p], obj2[p]) : obj2[p];

    return obj1;
}

merge(obj1, obj2 );
console.dir( obj1 ); // { x:1, y:{ a:1, b:2 } }

edited Nov 3, 2011 at 17:54

answered Nov 3, 2011 at 15:31

vsync

133k61 gold badges345 silver badges430 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

vsync Over a year ago

please REFACTOR this to the max

pimvdb Over a year ago

You should use continue instead of break to skip a property; currently it stops the complete loop if it encounters a non-existing property.

vsync Over a year ago

I have refactored my code since, to use 'prop IN obj' testing

pimvdb Over a year ago

I'm wondering why you don't use obj1.hasOwnProperty(p) as well. It's only about properties that obj1 has itself without the prototype ones.

vsync Over a year ago

=> I wonder if I could just settle with if( p in obj1 ) instead of the hasOwnProperty

Steve Campbell · Accepted Answer · 2011-12-22 19:54:19Z

0

Minor tweak to the solution, adding support for arrays (replace, not append - that would be harder):

function merge(obj1, obj2) {
    for( var p in obj2 )
        if( obj1.hasOwnProperty(p) )
            obj1[p] = (typeof obj2[p] === 'object' && !(p.length)) ? merge(obj1[p], obj2[p]) : obj2[p];

    return obj1;
}

answered Dec 22, 2011 at 19:54

Steve Campbell

3,6452 gold badges34 silver badges44 bronze badges

Collectives™ on Stack Overflow

merge JSON objects without new keys

Input

Output

2 Answers 2

5 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

Input

Output

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related